Exothermic welding has been widely employed in the formation of electrical connections or in the welding of steel such as rails and in joining reinforcing bar. The welding process utilizes powdered materials such as copper oxide and aluminum. The powdered material is placed in a crucible and ignited. Typically in electrical connections, the reduction of the copper oxide by aluminum produces molten copper and aluminum slag. Molten aluminum and molten iron may also be produced by related processes. The molten copper flows from the crucible over the parts to be welded. These parts are contained in a mold, melting them and welding them together. The slag of aluminum oxide which forms on top is removed and discarded. The process makes a high quality low impedance electrical connection. One typical application of this process is to make an electrical connection, such as a grounding connection, for example, to a steel column or fence post, or a connection where one of the conductors extends vertically. Welding metals or powders, and a wide variety molds and other related accessories to make these connections are sold under the registered trademark CADWELD.RTM. by Erico Inc. of Solon, Ohio.
Most typically the molds are formed by two semi-permanent graphite or ceramic blocks vertically split which are hollowed out to form the crucible, a receiving mold chamber for the pieces to be welded, and the interconnecting tap hole. The two mold blocks are opened and closed horizontally by a toggle action handle frame or clamp. Reference may be had to Burke U.S. Pat. Nos. 2,904,862 and 3,004,310 for illustrations of such exothermic cast welding mold assemblies. Where the mold parts are horizontally split, it is usual that the bottom of the block containing the crucible forms the top part of the mold while the other or lower part is hinged to separate from the top part. The two mold blocks are also supported for opening and closing by a toggle clamp opening and closing vertically.
A variety of mold supports may be employed to hold the mold assembly to a vertical surface. Typically a C-clamp, magnetic clamp, or even a chain sling or pipe clamp may be employed. Chain slings are typically used with mold assemblies for welding reinforcing bar such as shown in U.S. Pat. Nos. 3,234,603 and 3,255,498. In such patents the mold is in the form of a metal sleeve and separate molds are provided for the crucible and the tap hole or tundish, all of which may either be set one on top of the other or be held together by chain slings. The assembly and disassembly is time consuming, and more so in cramped quarters.
The semi-permanent molds may be cleaned and reused. Properly handled, used and cleaned, molds may make fifty or more connections. However, improperly used or cleaned molds have to be replaced more often. Also, the molds have to be replaced or changed for different types of connections. There are literally dozens of types of connections and within each type of connection classification there are a wide number of conductor size variations. Also, the weld metal or powder is carefully pre-packaged by size. While the mold forming parts which receive the parts to be welded and which form the weld, need to be carefully designed and machined, that is not necessarily true of the crucible, and yet the crucible may form the largest portion of the mold system. Where the mold part and crucible are formed from a common block of graphite, excessive wear or damage to any part of the mold part requires that the entire mold be discarded even though the crucible is still usable. In some situations, a different type of crucible may be required, such as one with an emissions filter, and as manufactured and sold by Erico, Inc. of Solon, Ohio under the registered trademark EXOLON.RTM. . Accordingly it would be advantageous to have a system where the crucible was separate from the mold forming parts and both the mold parts and crucible could be readily changed or substituted, while at the same time positioning and handling the crucible and mold parts for quick and convenient operation and cleaning for reuse.
If the crucible and mold are separable, it is important that when assembled they be held together with the proper degree of force so that no molten metal leakage occurs, and yet not too much force which might damage the mold parts, particularly if foreign matter is in the interface. It is also important that such force be quickly applicable or released, and readily adjustable. It is also important that when the jig is open, it not be loose. Looseness or slippage makes it more difficult to achieve proper conductor placement and to clean the molds after the weld.
It is also important that the jig or frame for holding the mold parts be low cost, able to separate and yet lock the mold parts quickly, and to hold the crucible for opening and closing travel, and for convenient cleaning, all while hot.